1. Field
Apparatuses and methods consistent with exemplary embodiments relate to surveillance cameras and systems.
2. Description of the Related Art
Surveillance cameras basically operate in two different modes: a day mode and a night mode.
Most surveillance cameras irradiate infrared rays to a photographing target region in the night mode. Also, a switching-type infrared blocking filter is installed in an optical system of the surveillance camera.
In the day mode, infrared rays are not irradiated as the infrared blocking filter is used, and thus, color image data is output.
In the night mode, infrared rays are irradiated as the infrared blocking filter is not used, and thus, black-and-white image data is output.
In the surveillance camera according to the related art, the illuminance of visible rays in a photographing target region is sensed by an illuminance sensor to which the infrared blocking filter is fixedly attached.
When the illuminance sensed by the illuminance sensor is lower than a fixed reference illuminance, the surveillance camera operates in the night mode, and when the illuminance sensed by the illuminance sensor is not lower than the fixed reference illuminance, the surveillance camera operates in the day mode.
The surveillance camera according to the related art has the following problems.
The wavelength of visible rays is about 380 nm to about 770 nm, and the wavelength of infrared rays is about 780 nm or more. Accordingly, the infrared blocking filter attached fixedly to the illuminance sensor of the surveillance camera may not completely block the infrared rays to be irradiated in the night mode.
Thus, when an object approaches the surveillance camera in the night mode, a large amount of infrared rays may be reflected from the object to be incident on the illuminance sensor. In this case, the surveillance camera may be switched to the day mode even at night.
Thus, there may occur a haunting phenomenon in which the surveillance camera is again switched to the night mode when the irradiation of infrared rays is stopped in a state where the surveillance camera is switched to the day mode at night, and then the surveillance camera is again switched to the day mode when the irradiation of infrared rays is started in a state where the surveillance camera is switched to the night mode. The haunting phenomenon may be more severe when the object includes a glass material or a mesh shape.
Due to the haunting phenomenon in which mode switching is repeated at night, a phenomenon in which a surveillance screen is brightened and then darkened may be repeated. Accordingly, when an object having a high infrared reflectance approaches the surveillance camera at night, a surveillant watching the surveillance screen may not quickly detect the object.